The present invention relates to a method and device for exchanging gas molecules between a gaseous medium and a liquid medium. More specific embodiments of the invention relate to improved methods and devices for gas transfer in applications such as blood oxygenation in heart-lung machines and gas scrubbing.
Vascular and parenchymal heart and lung diseases represent a major disease burden, socioeconomic problem and are frequent cause of death. Their growing incidence associated with the aging population stimulated research activities with respect to better methods of prevention, diagnosis and treatment. These activities also include the development of improved heart-lung machines. Nowadays extracorporal circulation during open heart surgery or lung operation has developed into a routine procedure. In order to supply the body with sufficient oxygen a heart-lung machine takes over the heart's pumping action and the lung's gas exchange function during surgeries.
One vital component of a heart-lung machine is the oxygenator. Blood that would normally return to the heart through the venae cavae, flows to the oxygenator for oxygenation, carbon dioxide removal, temperature regulation and anesthetic exchanges. The oxygenated blood then returns to the patient, typically through the aorta, bypassing the heart and lungs completely. A membrane oxygenator as currently used consists of a gas-permeable membrane, typically made of multilayered membrane sheets of microporous polypropylene, silicone rubber, or thousands of silica, polypropyleneor polyethylene capillaries. To achieve a large gas exchange capacity, gas and blood flow on opposite sides of the membrane, permitting the blood cells to adsorb oxygen molecules directly.
Unfortunately, all synthetic materials display a more or less pronounced incompatibilty with blood. Contact with the artificial surface can induce hemolysis, protein denaturation and platelet and leukocyte damage and thrombosis. In order to reduce the incompatibility, heparin can be added to blood or the components of the blood circuit can be provided with a heparin coating. Heparin, either as a coating or as a blood additive, reduces the damage to the blood during extracoporal circulation and the deposition of fibrin or platelets on the surface of the membrane. Such a deposition greatly reduces the gas exchange rate.
Lately, superhydrophobic surfaces such as superhydrophobic Teflon tubes were tested for their ability to prevent attachment of blood, platelets, and blood components such as proteins under stationary or flow conditions. However, the results were not encouraging. Due to the low interfacial tension of blood (γ=0.047 N/m), blood easily impales a superhydrophobic surface, resulting in an increased contact area with the substrate.
Porous polymer membranes are also used in various gas scrubbing applications. For example, acidic gases such as CO2, SO2, SO3, and H2S are extracted from process and waste gases by contacting these gases via a gas-permeable membrane with a liquid medium such as an aqueous solution of amines which is capable to absorb the acidic gases and, thus, to remove the same from the process or waste gases. The gas-exchange capacity of these membranes tends to be impaired by the insufficient chemical long-term resistance of most of the polymeric membranes commercially available and also by a gradual wetting of the membranes which increases the resistance to mass transfer and may decrease the process efficiency dramatically. Other gas scrubbing processes face similar problems or suffer from a low efficiency.
WO 2011/001036 suggests to use superamphiphobic aerogels as selective membranes which can be permeated by vapours and gases but not by a liquid such as water, e.g. in gas extraction from liquids. The aerogels disclosed therein represent bicontinuous materials which are extremely light weight, highly porous and mechanically rather instable. In particular, their superamphiphobic properties, repellency of both water and oils, cannot be maintained if the aerogel is subjected to a mechanical force such as a hydrostatic pressure, in particular a pressure above about 1000 Pa.
In view of the drawbacks of the prior art, the main object of the present invention was to provide improved methods and devices for transferring gas molecules from a gaseous medium into a liquid medium of low surface tension or vice versa, in particular in applications such as blood oxygenation in heart-lung machines, and gas scrubbing.
This objective has been achieved by providing the novel methods for gas transfer and the devices according to the invention.